Ag Nanorings Research Articles

A simple and highly efficient route to the synthesis of NaLnF4–Ag hybrid nanorice with excellent SERS performances

This paper reports the synthesis of a new class of NaLnF(4)-Ag (Ln = Nd, Sm, Eu, Tb, Ho) hybrid nanorice and its application as a surface-enhanced Raman scattering (SERS) substrate in chemical analyses. Rice-shaped NaLnF(4) nanoparticles as templates are prepared by a modified hydrothermal method. Then, the NaLnF(4) nanorice particles are decorated with Ag nanoparticles by magnetron sputtering method to form NaLnF(4)-Ag hybrid nanostructures. The high-density Ag nanogaps on NaLnF(4) can be obtained by the prolonging sputtering times or increasing the sputtering powers. These nanogaps can serve as Raman 'hot spots', leading to dramatic enhancement of the Raman signal. The NaLnF(4)-Ag hybrid nanorice is found to be robust and is an efficient SERS substrate for the vibrational spectroscopic characterization of molecular adsorbates; the Raman enhancement factor of Rhodamine 6G (R6G) absorbed on NaLnF(4)-Ag nanorice is estimated to be about 10(13). Since the produced NaLnF(4)-Ag hybrid nanorice particles are firmly fastened on a silicon wafer, they can serve as universal SERS substrates to detect target analytes. We also evaluate their SERS performances using 4-mercaptopyridine (Mpy), and 4-mercaptobenzoic acid (MBA) molecules, and the detection limit for Mpy and MBA is as low as 10(-12) M and 10(-10) M, respectively, which meets the requirements of the ultratrace detection of analytes. This simple and highly efficient approach to the large-scale synthesis of NaLnF(4)-Ag nanorice with high SERS activity and sensitivity makes it a perfect choice for practical SERS detection applications.

Synthesis of silver nanorings by atom beam sputtering

Silver nanorings, evident by transmission electron microscopy and atomic force microscopy, were synthesised through self-assembly of Ag nanoparticles embedded in silica by atom beam co-sputtering. Optical absorption studies revealed localised surface plasmon resonance (LSPR) at ~430 nm, which is in close agreement with our theoretical calculations. The dimensions of nanorings were found to be substrate dependent, which indicates that the diffusivity of Ag plays an important role in the self-assembly process. The Ag nanorings formation has been explained in terms of stress evolution in aggregates of Ag nanoparticles at surface, due to irradiation with energetic sputtered atoms.

Scattering focusing and localized surface plasmons in a single Ag nanoring

We investigate the far-field scattering property of a single Ag nanoring. Under oblique excitation, two-focus scatterings with distinct intensities were observed. We show that the two-focus scatterings result from the interference of far-field scattering light from the ring circumference, and the local field enhancement effect of surface plasmons plays the key role in the focus intensity. By finite difference time domain and numerical integer methods, we calculated far-field scattering and surface plasmons’ distributions, and the results are in good agreement with the experiment.

Multipolar Plasmon Resonances in Individual Ag Nanorice

We study the optical excitation of high-order surface plasmon resonance modes in individual Ag nanorice particles using dark-field scattering spectroscopy. We analyze the results by model calculations using the boundary element method. Symmetry breaking caused by oblique illumination makes the even order resonance modes observable in the optical spectrum. All the resonance peaks are found to redshift with increasing length of the particle.

Surface plasmons amplifications in single Ag nanoring

The stimulated amplifications of surface plasmons (SPs) propagating along a single silver nanoring is theoretically investigated by considering the interactions between SPs and activated semiconductor quantum dots (SQDs). Threshold condition for the stimulated amplifications, the SP density as a function of propagation length and the maximum SP density are obtained. The SPs can be nonlinearly amplified when the pumping rate of SQDs is larger than the threshold, and the maximum value of SP density increases linearly with the pumping rate of SQDs.

A simple approach for large-area fabrication of Ag nanorings

A simple and low-cost method based on a two-step heat treatment ofAgNO3/SiO2 film has been developed for fabricating metal Ag nanoring arrays. The as-preparednanorings have an inner diameter of 70–250 nm and an average wall thickness (namelywire diameter) of approximately 30 nm with a number density of approximately109 cm−2 on thesurface of the SiO2 matrix. X-ray diffraction (XRD) results reveal that these nanorings exhibit aface-centered cubic crystal structure. Furthermore, a new growth mechanism,namely a molten metal bubble as a self-template, is tentatively proposed for Agnanorings.